(a) Technical Field
The present disclosure relates, generally, to an apparatus and method for controlling motor position and creep of an electric vehicle.
(b) Background Art
In a typical gasoline engine vehicle, the idle torque of an engine is transmitted to a torque converter and a transmission even when an accelerator pedal and a brake pedal are not depressed while the vehicle is running, and thus the vehicle runs in a creep mode (creep running) which allows the vehicle to slowly move at a low speed.
For example, as shown in FIG. 11, a vehicle running on a slope encounters a slope resistance of mgsinθ as well as a rolling resistance. Due to such a slope resistance, the vehicle is stopped on the slope by friction brake force generated by a driver's operation of the brake pedal, and then, upon release of the brake pedal, the vehicle may roll backwards.
To get out of this situation, the driver tries to prevent the vehicle from rolling backwards, by depressing the brake pedal again or depressing the accelerator pedal.
In order to eliminate the inconvenience of having to try to prevent the vehicle from rolling backwards on a slope, creep control technology has been introduced, which prevents the vehicle from rolling by maintaining a predetermined amount of friction brake even when the accelerator pedal and the brake pedal are not depressed, and then releases the friction brake when the driver depresses the accelerator pedal again to switch to a normal driving condition.
On the contrary, an electric vehicle equipped with a fuel cell runs only by a motor driving system (a motor, a decelerator, and wheels) without an engine. Thus, no idle torque is automatically generated by the motor when the vehicle is stopped, and no creep occurs, different from a gasoline engine vehicle.
Accordingly, it is necessary to implement a creep function by controlling motor torque in order to provide the creep function of the gasoline engine vehicle to the electric vehicle.
Preferably, a pure electric vehicle, such as a fuel cell vehicle, driven by a motor requires a creep control algorithm for generating a torque like an engine idle torque in order to offer the same driving feeling as a typical mass-produced gasoline vehicle. Along with the development of the creep control algorithm for improving driving feeling during creep running, the technology for preventing the vehicle from rolling backwards on a slope upon restart after a stop has been studied.
In examples of vehicles driven only by a motor, such as a fuel cell vehicle and an electric vehicle, the prevention of backward rolling on a slope can be implemented simply by controlling the motor driving force (for example, by a method of increasing a motor driving torque upon detection of a slope) without introducing any additional system.
For example, as shown in FIG. 10, it is possible to implement a method of detecting a slope by applying a slope angle sensor or a rolling determination algorithm to a fuel cell vehicle and an electric vehicle and increasing a motor torque based on the detection result. This method can be easily implemented because it is easy to control the motor driving force.
However, it is necessary to calculate the amount of motor torque required additionally, and the calculated amount should be varied depending on a number of variables, such as slope angle, number of passengers, etc. Therefore, many allowances and tests are needed.
In particular, in the case where a slope is detected while maintaining a conventional creep torque control logic, the method of increasing the creep torque command may have difficulties in calculating the correct amount of additional motor torque to be suitably increased and keeping the vehicle in a correct position. Further, if a given condition, such as the number of passengers, slope angle, etc., changes, the amount of motor torque has to be calculated again in order to maintain the vehicle position. Otherwise, the vehicle may roll backwards or rush forward too much.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.